Recently, catalytic coating mixed with a metal oxidant having excellent photocatalytic function in contamination resistance and antibacterial property have drawn attention.
Coatings used for exterior walls of buildings, vehicle steel plate, canvas and others, is desired to have an excellent appearance, and less adhesive characteristic against dirt, including rain marks, i.e. contamination resistance (environmental contamination).
For this reason, there is sought a method for effectively utilizing coating material and surface finishing material (hereinafter, referred to as together as “coating” or “coatings”) which have excellent hydrophilic properties and provides contamination resistance and antibacterial properties. When a metal oxide having photocatalytic function is mixed as a coating, a hydrophilic resin binder (hydrophilic polymer) is generally used to fully enhance the photocatalytic function against environment contamination.
Further, since the photocatalytic function excites an extreme redox reaction to dissolve organics, it also dissolves an organic resin binder mixed as a coating, thereby causing a problem of deterioration and poor durability of the coating film.
Therefore, a glassy inorganic binder called a silica sol is usually used, when the photocatalytic coating is mixed.
A patent application already has been filed for a photocatalytic coating which includes a silica sol and is excellent in dispersion stability (for example, Japanese Patent JP-A-H11-343426 (Pages 1 to 5)).
Further, a patent application has been filed for a titanium oxide coating composition using a silica sol as a binding material which is not deteriorated as a result of a photocatalytic reaction (for example, Japanese Patent JP-A-2000-73297).